Choosing a method to measure your plot depends on the intended use and the size of the parcel. DIY methods range from using mobile apps to taking manual measurements on site. For larger and more complex projects, it is advisable to hire a professional land surveyor.
Measurement using Satellite Imagery
Web mapping platforms like Google and Bing Maps are generally used for online measurement of land. They use satellite imagery to form near precise representations of the topography of the earth. With this tool, we can measure linear distances and areas of a plot on any part of the globe.
On a Mobile Device
There are many applications available on Android and iOS devices that can be used for measurement of plots. For demonstration, let us take the example of the Google Earth app that is available for free on the App store.
Step 1
Locate the plot of land on your device. You can do this by panning manually or by keying in the coordinates or name of the nearest landmark.
Step 2: Distance
Tap the ‘Measure tool’ button on the top right part of the screen. Move the crosshair to the first point and tap the ‘Add point’ button. Move the crosshair to the next point and tap ‘Add point’ again. The measurement will be displayed along the connecting line.
Step 3: Area
To find the area of the plot, tap ‘Add point’ at all boundary junctions to form a closed polygon. Tap on ‘Close shape’. The perimeter and area will be shown at the bottom of the screen. You can choose units as preferred.
On a PC or desktop
The procedure for measuring on a computer is similar to that on mobile devices. Websites like Zoom Earth, Google and Bing Maps helps to measure distances and area. So does applications like Google Earth Pro. For demonstration, let us use the Zoom Earth website service.
Step 1
Locate the plot of land in the Zoom Earth interface.
Step 2: Distance
Click on the ‘Measure distance’ button (5th) on the right side of the screen.
Click on a point to start measuring and add points at every junction.
Double-click to complete and display the total distance.
Step 3: Area
Click on the ‘Measure area’ button (6th) on the right side of the screen.
Click on a point to start measuring and add points at every junction.
Double-click to complete and display the total area.
Web mapping platforms are simple to use. They are effective for quick measurements from the comfort of our devices. But, there is a limit to its accuracy:
- The points we choose on screen may not exactly be over the boundary markers.
- The view of the plot and its boundaries can be blocked by clouds or tree cover.
- Precision inaccuracy of satellite imagery.
Hence, we move on to a more hands-on method to measure a plot of land:
Manual measurement on-site
DIY Physical measurements of plots are easier when the areas are roughly equal to or less than 1000sqm. This can be done with the help of a tape measure and simple geometric formulas. Larger areas can be surveyed using Laser measuring devices and measuring wheels.
Triangulation Method
Plots of land are seldom perfect rectangles in the real world. They are usually ‘irregular polygons’ of three or more sides. The trick here is to completely divide the polygon into the least number of triangles. Areas for each of these triangles is then calculated and summed up to find the total area of the plot.
Step 1
Establish the end points of the boundary on the plot. These may be in the form of wooden stakes, stones or metal pipes depending on practices in your locality. You may even already have a fenced yard. Measure and note down the distance between each of these points using a tape measure or wheel.
Step 2
Divide the plot into triangles between these endpoints. Measure and note down the distance of the diagonals formed between the end points.
Step 3
Calculate the area of each of the triangles using the formula:
Where a, b and c are the dimensions of the sides of the triangle and,
Alternatively, you could input the values into an online area calculator to find the area.
Step 4
Add the areas of individual triangles to find the total area of the site.
Calculating the size of a plot by manual triangulation is far more accurate than using satellite imagery. This method works well for measuring space for a vegetable patch or a backyard landscape. You could even get satisfactory results for small to medium sized plots of quarter of an acre. The only minor drawbacks are that it takes time, effort and requires basic tools.
But what happens when the plot to measure is larger and more complex? The land could have level differences and topographic features like boulders & large pits. There could be dense vegetation and inaccessible zones. Such a situation would be difficult to overcome with a measuring tape and a sketch pad.
This is when we know it is time to call in the services of a Professional Surveyor.
Professional Land Survey
A professional survey is done by licensed surveyors using sophisticated tools and machinery. These surveys provide us with a precise drawing of the site. Beyond area and dimension, it also shows locations of various features on and immediately off the site.
Total Station Survey
This method uses the same logic of ‘triangulation method’ as seen in the previous section. An Electronic Theodolite device (Total Station) is placed at a central part of the site. Prism reflectors are then moved between different end points of the boundary.
Infrared signals originating from the total station get reflected back from these prisms. These signals get recorded by the total station which is later interpreted by a computer.
Using triangulation, the computer provides an accurate drawing of the surveyed area. This can be used to read precise distances, areas & topography and locate physical features.
You may have seen Total Stations in action in industries like construction and infrastructure. They are currently one of the most commonly used methods for mapping. But, they are time & effort consuming especially in the data collection stage.
This brings us to a relatively new player to the mapping field:
Drone Survey
These surveys use ‘Unmanned Aerial Vehicles (UAV)’ or drones to do fly-bys and take multiple images of a plot. These images are then ‘stitched’ together by apps built for the purpose. This output can then be used to measure distances and areas.
With the increasing affordability of drones, surveying can even be done without the help of a professional. Quad copters like DJI’s Phantom series and Mavic Pro coupled with a Smartphone can take accurate survey of a plot.
The Survey Process
It is a fairly simple process where the drone flies over a predetermined trajectory at a particular altitude. This is controlled by apps such as Drone Deploy and Data Mapper.
During this flight, the drone captures high resolution images. These are uploaded to web services or apps that process this raw data to provide measurable 3d models.
A tract of land of roughly 10,000sqm in area would take around 10 minutes to scan at an altitude of 10 meters. This makes drone surveys one of the fastest and cheapest means of plot measurements available today.
To reiterate from where we started off:
Choosing a method to measure your plot depends on the intended use and the size of the parcel.
For a rough estimate of dimensions and area, satellite imagery is the way to go.
For a more accurate measurement of small to medium parcels of land, choose manual triangulation.
For a large tract of land with complex factors involved, opt for the professional services of Total Station or Drone surveyors.
References:
Arango, C. &. (2015). COMPARISON BETWEEN MULTICOPTER UAV AND TOTAL STATION FOR ESTIMATING STOCKPILE VOLUMES. ISPRS – International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences.
Buczkowski, A. (2017). Step by step guide to complete your first drone mapping project. Retrieved from Geo Awesomness: https://geoawesomeness.com/step-step-guide-complete-first-drone-mapping-project/
City of Bloomington MN. (2015). How Does Land Surveying Work? Retrieved from https://www.youtube.com/watch?v=q20-DBAmm2E
Drone Deploy. (n.d.). Product Details. Retrieved from Drone Deploy: https://www.dronedeploy.com/product/analysis/
ICSM, Australia. (n.d.). Surveying Methods. Retrieved from https://www.icsm.gov.au/education/fundamentals-mapping/surveying-mapping/surveying-methods
Music, S. S. (2019). Apply the procedure of triangulation to estimate the extent of land. Retrieved from https://www.youtube.com/watch?v=F6ZZBQG_PtU
Penn State, Dept. of Georgraphy. (2012). Land Surveying and Conventional Techniques for Measuring Positions on the Earth’s Surface. Retrieved from https://www.e-education.psu.edu/geog160/node/1926
